GBT Development Program
The Path to Discovery: A Continually Evolving Instrument
The GBT was designed to allow ready upgrades and changes to all aspects of its hardware and software. A specialty (or PI-driven) instrument can be installed on the telescope with relative ease, making it feasible for an individual or group of researchers to outfit the telescope to meet their particular science goals. The GBT also has a vigorous development program in collaboration with college and university groups to take advantage of the latest technology and provide our user community with a constantly improving facility. Development projects will continue through the coming decade and have already led to important discoveries in a number of areas.
The Path Forward
Imaging the Radio Universe - Camera Development: The NRAO camera development program is a collaboration between the NRAO and more than 20 university, college, and industry groups to design, develop, and build a suite of radio cameras that will increase the GBT’s capabilities dramatically. Three types of instrumentation are planned: conventional feed horn arrays, phased array receivers, and bolometer arrays. The science achievable with these new instruments on the GBT is extraordinary and varied: rapid, sensitive maps of outflows from comets and of molecular clouds in nearby galaxies; studies of pre-biotic molecules and chemical processes throughout the Galaxy; study of hot gas in galaxy clusters to compliment X-ray images and reveal how cosmic structures form and evolve; and uncovering the most distant galaxies from the emission of cold dust and redshifted molecular lines. In addition, the cameras will improve capabilities for pulsar searches and very deep observations of HI that trace past galaxy interactions. The power and flexibility of these instruments will make possible experiments that cannot now be done on any telescope.
Focused Science Instruments - Optimized Single/Dual Pixel Feeds: In addition to cameras, is it important to develop receiver systems optimized to a given science case which can be rapidly put into operation on the GBT. Currently there are three such instruments in development – a 4mm two-pixel receiver for molecular line and VLBA studies, a wide-bandwidth receiver optimized for the NanoGrav Gravitational Wave detection pulsar experiment at 15cm, and a broadband receiver covering 12-18 GHz for the detection and study of pulsars in the Galactic Center.
Cyberdiscovery - Software, Algorithm Development, and High Performance Computing: Discovering the unusual or unexpected in scientific data is often the path to the most fundamental breakthroughs. Yet as scientific data become more complex, our ability to find the unexpected is rapidly diminishing. New scientific instruments will regularly create data sets of 50-100 TB or more in a single observing project, data sets which are far too large to be examined using existing methods. Yet close scrutiny of the data is required to discover unexpected signals or unusual events. A paradigm shift must occur in the approach used to view and analyze these massive data sets. NRAO is teaming with university, industry and other national laboratories to research, design, and test the algorithms and tools needed for modern data analysis.
Maximizing the Science – Improved Telescope Performance and Infrastructure: The GBT development program is not limited to new instrumentation and software to meet individual scientific goals. NRAO staff also work with the community to ensure the GBT performance and infrastructure is sufficient to meet future scientific demands. The completion of a digital servo system in 2011 will allow for improved motions of the GBT, increasing the telescope pointing and observing efficiencies at high frequencies while providing significantly improved baselines and sensitivities for projects in all frequency ranges. Continued upgrades to the surface modeling and better understanding of the weather effects on telescope performance will increase the number of good weather hours available for high frequency observing from the roughly 2,000 scheduled high frequency (>18 GHz) hours in 2010 to 3,000 hours or more.
The signal processing and data transmission of the GBT is also being improved to provide higher sensitivity, increased bandwidth, and improved flexibility for all GBT science. The Configurable Instrument Collection for Agile Data Acquisition program (CICADA) is an NRAO collaboration with the University of California at Berkeley, Xilinx Inc, and many university groups around the world. The CICADA program is developing digital signal processing and data transmission systems using reconfigurable off-the-shelf hardware platforms and software tools that allow rapid design, verification, and deployment of astronomical signal processing systems. The program is based on hardware and tools developed by U.C. Berkeley's CASPER group. The CICADA collaborators are working with the CASPER hardware and software to research, define, and implement astronomical signal processing systems that have numerous applications. This work will allow development of detectors that can encompass the entire band of a radio camera at high frequency resolution, improving the throughput of the GBT by an order of magnitude. A new data transmission system will also improve instrumental stability and reduce instrumental effects for the most sensitive observations.
Preserving the Radio Sky - RFI Mitigation and Excision: Cosmic radio signals are easily masked or confused by man-made interference: a cellular telephone on Mars would produce a signal on Earth stronger than most astronomical sources studied with the GBT. The NRAO Green Bank Observatory is located within two RFI protection zones - the federal National Radio Quiet Zone (NRQZ) and the West Virginia Radio Astronomy Zone (WVRAZ), that provide protection against new sources of terrestrial interference. Nonetheless RFI remains a problem due to leakage from transmitters outside the zones, satellites, and from unregulated devices. As a result RFI excision techniques are increasingly important. NRAO aims to take advantage of the digital signal processing work being done for the GBT to develop, test, and implement a variety of RFI excision techniques. This will enable sensitive observations to be made at frequencies now compromised by interference and directly aid the study of baryon acoustic oscillations, pulsar timing, and highly redshifted lines of HI and OH.
